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Showing posts with label HTML5. Show all posts
HTML5 Data Storage
HTML5 Data Storage



function supports_html5_storage() {
                try {
                    return 'sessionStorage' in window && window['sessionStorage'] !== null;
                } catch (e) {
                    return false;
                }
            }
            alert(supports_html5_storage());
5:27 AM
HTML5 LocalStorage
HTML5 LocalStorage

This tutorial assumes that you are already familiar with HTML5  localStorage.

Although HTML5  localStorage is very useful, its usage is restricted to key value mechanism. Key and value is stored in string format despite what we need. For an instance, though you can specify a boolean type (either true or false) as the value, it is stored as a string.

What if we need to store multiple items as the value for a certain key. This can be little bit tricky if you gonna place an array directly as the value. When we scratch the surface of localStorage basic principles this is not possible. However you can come up with your own solutions that might work for you.

This tutorial demonstrates a simple way of handling above problem using json. We gonna store array as a json string. So nothing new here.

First add jQuery library as we are using some jQuery functions.


<script type="text/javascript">
 var favorites_str = localStorage.getItem('my_favorites');
 if(favorites_str == null) {
 favorites = [];
 favorites.push({ "name":"keshi", "id":"6" });
 } else{
 favorites = JSON.parse(favorites_str);
 favorites.push({ "name":"sara", "id":"6" });
 
}
 localStorage.setItem('my_favorites',JSON.stringify(favorites));
 </script>

To verify that above script is functioning please copy and run below script. It will make things easy, if you put this code in  a separate file.

<script type="text/javascript">
 var data = localStorage.getItem('my_favorites');
 if(data == null){
 alert("0 favorites");
 }else{
 favorites = JSON.parse(data);
 $.each(favorites, function(index,item){
 alert(item.name);
 
});
 }
 </script>
3:47 AM

HTML5 Data Storage
HTML5 Data Storage

HTML5 supports client side data storage. There are several types of storing data with HTML5

1. local storage through localStorage object

2. session storage through sessionStorage object

3. SQL based database

This tutorial demonstrates how to manage a client side SQL based database with HTML5.

Demo


<!DOCTYPE html>
<html>
    <head>
        <meta name=viewport content="user-scalable=no,width=device-width" />
        <link rel="stylesheet" href="css/jquery.mobile-1.1.0.min.css" />
        <script src="js/jquery-1.7.2.min.js"></script>
        <script src="js/jquery.mobile-1.1.0.min.js"></script>
    </head>
    <body>
        <div data-role=page id=home>
            <div data-role=header>
                <h1>Home</h1>
            </div>
 
            <div data-role="content">
                <a href="#" data-role="button" id="create"> Create table </a>
                <a href="#" data-role="button" id="remove"> Delete table </a>
                <span> Item </span>
                <input type="text" id="item">
                <span> Quantity </span>
                <input type="text" id="quantity">
                <a href="#" data-role="button" id="insert">Insert item</a>
                <a href="#" data-role="button" id="list">List items </a>
 
                <ul data-inset="true" data-role="listview" id="itemlist"></ul>
            </div>
        </div>
 
        <script>
            var db = openDatabase ("itemDB", "1.0", "itemDB", 65535);
            $("#create").bind ("click", function (e)
            {
                db.transaction (function (transaction)
                {
                    var sql = "CREATE TABLE items " +
                        " (id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, " +
                        "item VARCHAR(100) NOT NULL, " +
                        "quantity int(2) NOT NULL)"
                    transaction.executeSql (sql, undefined, function ()
                    {
                        alert ("Table created");
                    },error
                );
                });
            });
 
            $("#remove").bind ("click", function (e)
            {
                if (!confirm ("Delete table?", "")) return;;
                db.transaction (function (transaction)
                {
                    var sql = "DROP TABLE items";
                    transaction.executeSql (sql, undefined, success, error);
                });
            });
 
            $("#insert").bind ("click", function (event)
            {
                var item = $("#item").val ();
                var quantity = $("#quantity").val ();
                db.transaction (function (transaction)
                {
                    var sql = "INSERT INTO items (item, quantity) VALUES (?, ?)";
                    transaction.executeSql (sql, [item, quantity], function ()
                    {
                        alert ("Item created!");
                    }, error);
                });
            });
 
            $("#list").bind ("click", function (event)
            {
                $("#itemlist").children().remove()
                db.transaction (function (transaction)
                {
                    var sql = "SELECT * FROM items";
                    transaction.executeSql (sql, undefined,
                    function (transaction, result)
                    {
 
                        if (result.rows.length)
                        {
                            for (var i = 0; i < result.rows.length; i++)
                            {
                                var row = result.rows.item (i);
                                var item = row.item;
                                var quantity = row.quantity;
                                $("#itemlist").append("<li>" + item + " - " + quantity + "</li>");
                            }
                        }
                        else
                        {
                            $("#itemlist").append("<li> No items </li>");
                        }
                    }, error);
 
                });
 
            });
 
            function success ()
            {
            }
 
            function error (transaction, err)
            {
                alert ("DB error : " + err.message);
                return false;
            }
        </script>
    </body>
 
</html>


Please note that Firefox does not support this type of web SQL databases. If you try this in a FF browser, it will throw "ReferenceError: openDatabase is not defined".
3:24 AM
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